A common industrial process for producing an amide compound involves Beckmann rearrangement of a corresponding oxime compound, using concentrated sulfuric acid and oleum in an industrial scale. However, such strong acid must be used in stoichiometric amounts or more, which causes generation of a large amount of ammonium sulfate as a byproduct during neutralization. The process, therefore, requires facilities for producing concentrated sulfuric acid and oleum and for treating ammonium sulfate, which is a process with significant environmental burden and facility cost (Patent Document No. 1, Patent Document No. 2).
Recently, Beckmann rearrangement which does not require sulfuric acid or oleum in a large amount has been intensely investigated. There have been described processes utilizing as a catalyst a strong acid such as a mixture of an ammonium salt of rhenium peroxide and trifluoromethanesulfonic acid (Non-patent Reference No. 1), indium triflate (Non-patent Reference No. 2) or ytterbium triflate (Non-patent Reference No. 3). There have been further described processes utilizing a combination of an acid and a dehydrating agent, including a process where the rearrangement reaction is conducted using N,N-disubstituted amide compound as a solvent, phosphorus pentoxide or a condensed phosphoric compound and a non-fluorine containing sulfonic anhydride or sulfocarboxylic anhydride (Patent Document Nos. 3 and 4) and a process using a zeolite catalyst pretreated with an aqueous acid-containing solution (Patent Document No. 5). As a process without an acid, there have been described a process conducting the rearrangement reaction in the presence of a combination of a rhenium compound and a nitrogen-containing heterocyclic compound (Patent Document Nos. 6 and 7) and a process comprising using zinc oxide (Patent Document No. 8). Patent Document No. 9 describes a process where using cyanuric chloride (also known as trichlorotriazine) as a dehydrating agent in a carboxylic acid solvent, an oxime is reacted with a carboxylic acid to produce an ester, which is then rearranged. Patent Document No. 10 describes a process where a hydrochloride of an oxime is rearranged using, for example, cyanuric chloride (also known as trichlorotriazine) as an initiator. Although some processes using a catalyst such as those described above can give a high rearrangement yield, the processes employ a particular catalyst or solvent for which a recovering or recycling method has not been explicitly described and are thus imperfect as an industrial process.
Patent Document No. 11 describes a process in which an oxime compound undergoes Beckmann rearrangement in a polar solvent, using, as a rearrangement catalyst, an aromatic-ring containing compound, which (1) contains, as an aromatic-ring member, at least one carbon atom having a leaving group and (2) as aromatic-ring members, at least three heteroatoms and/or carbon atoms having an electron-withdrawing group and in which (3) two of the heteroatoms and/or the carbon atoms having an electron-withdrawing group are in ortho or para position to the carbon atom having a leaving group. Non-patent Document No. 4 also describes a similar approach.
Furthermore, Non-patent Document No. 5 has described that a phosphate having a heterocyclic structure similar to that of a catalyst described in Patent Document No. 11 is active as a catalyst for Beckmann rearrangement. Patent Document No. 12 has described that Beckmann rearrangement can be conducted in a nonpolar solvent, using a catalyst disclosed in Patent Document No. 11 and Non-patent Document No. 4. Patent Document Nos. 13 and 14 have described a process for Beckmann rearrangement of an oxime compound using a compound analogous to a catalyst disclosed in Patent Document No. 11.
Patent Document Nos. 15 and 16 describes Beckmann rearrangement of an oxime compound using thionyl chloride as a catalyst.
Among the catalysts for Beckmann rearrangement described in the above prior art documents, those that are relatively inexpensive and readily available as industrial chemicals include cyanuric chloride, phosphorous trichloride, phosphorous pentachloride, thionyl chloride and sulfuryl chloride. Among these, cyanuric chloride, phosphorous trichloride and phosphorous pentachloride are converted, when inactivated, into compounds insoluble in an organic solvent such as cyanuric acid and phosphoric acid, and therefore when being used in a large amount, they cause pipe blockage or poor heat transfer in an industrial process, and thus they are undesirable. Furthermore, phosphorous trichloride and phosphorous pentachloride are environmentally undesirable because of their severe toxicity.
In contrast, thionyl chloride is a catalyst suitable for industrial application because it is decomposed to give hydrogen chloride and sulfur dioxide without solid precipitation. Patent Document Nos. 15 and 16 disclose a process in which thionyl chloride and an oxime compound are mixed and heated, and it has been found that in the process, a yield varies depending on some factors such as a rate of temperature increase and a yield itself is low. Furthermore, Beckmann rearrangement is so exothermic that it cannot be controlled by the process described in Patent Document Nos. 15 and 16, which cannot be, therefore, applied to a larger industrial scale. There has been also found a problem that a desired amide compound cannot be produced with a high yield by the procedure in which thionyl chloride is added to a solution of an oxime compound heated to a predetermined temperature.